Normally, rolling cutter drill bits such as oil well bits, blast hole bits and mining bits, may be classified as either "sealed" or "unsealed" bits. The sealed bits, which are usually the premium line of bits, utilize elastomeric seals between the rotating cutters and the bearing journals to prevent intrusion of dirt, sand, rock cuttings, corrosive liquids and other contaminants into the bearing area. This reduction of detritus into the bearing area prolongs the life of the bearings and extends the drilling life of the bit. One such premium sealed bit having particularly good elastomeric journal bearing seals is that disclosed in U.S. Pat. No. 4,037,673, granted to Daniel B. Justman on July 26, 1977, which patent is herein incorporated by reference.
In the Justman patent, the drawing reveals a frustoconical rolling cutter 15 which is rotatably mounted on a bearing shaft 14 by bearings 18 and 19a. An elastomeric sealing ring 25 is located in an internal groove 24 in cutter 15 and sealingly engages shaft 14. The sealing ring can be an O-ring or be rectangular in cross-section, and is placed in hoop compression. The seal preferably is static with respect to the cutter and dynamic with respect to the shaft.
Although the Justman drilling bit sealing system is an improvement over the seals that were conventional at that time, such as that disclosed in U.S. Pat. No. 3,765,495, it does suffer from one disadvantage also affecting the other known bit sealing systems. Conventional bit seals utilize a dynamic interface between the elastomeric seal member and either the bearing journal, the cutter, or both. As a result of the continuous movement of the elastomeric seal against one or both of the metal elements, a rapid wear and deterioration of the seal surface usually occurs. Efforts to slow this wear and deterioration have included the shielding type of structure disclosed in the aformentioned Justman patent and a polishing of the metal faces which contact the seal to a high surface smoothness.
The present invention eliminates the elastomeric seal deterioration from sliding contact with metal surfaces by replacing the usual single elastomeric seal with a compound elastomeric and metal sealing system, with the metal component providing the dynamic seal against the rotating metal component in the bit.